(1) Field of the Invention
This invention relates to a constant pressure printing mechanism for use in a portable label printing machine, or the like.
(2) Description of the Prior Art
Prior constant pressure printing mechanisms have been complicated in structure with a large number of parts. This has led to frequent breakdowns. In addition, fine regulations or adjustments were required to control printing pressure. Therefore, substantial skill was required for the operation and maintenance of such prior constant pressure printing mechanisms and such skill was not ordinarily available at the point of use by unskilled store clerks, or the like.
With portable label printing machines which are not provided with a constant pressure printing mechanism, the darkness of the printed characters and the even toning or printing of labels depends upon the intensity of squeezing or operation of hand lever squeezing. Therefore, printing of characters of even intensity and stable toning or application of ink is quite difficult to attain. When the hand lever of such a label printing machine is squeezed strongly, the printed characters on the labels become very dark. On the other hand, when the hand lever is squeezed weakly, the printed characters on labels become faint. In addition, variations occur not only from label to label but also in the shading and toning of the printing on individual labels.
In recent years, P.O.S. (point of sales) systems have widely been employed in various commercial fields in which the information that is printed on labels is read out electro-optically and not by the naked eye. Therefore, precise and clear printing of labels has become essential in such cases.